Stereo cameras consist of two or more camera systems spatially offset from each other. Each camera captures an image of the same scene and subsequent analysis of the recorded images provides distance information in addition to standard two-dimensional images. The configuration mimics that of a pair of eyes. Humans perceive distance by comparing visual information taken in through the eyes. The distance between the eyes results in slight differences in the images formed in the two eyes. The brain processes this disparity to determine the distance to various objects in the scene and provide depth perception. Similarly, two cameras placed next to each other and viewing the same scene will capture slightly different images due to the distance between the two cameras. Objects from the scene will appear in slightly different positions in the images. If the cameras are spaced apart from each other by a known distance, the three-dimensional location of objects in the scene relative to the stereo camera can be determined from the captured images by triangulation. The triangulation is based on knowledge of (a) the positioning of the two cameras relative to each other and (b) the imaged locations of objects in the scene.
Stereo cameras are being found in an increasing number of applications requiring image capture and distance information for objects in the scene. For example, stereo cameras are being implemented in cars to help prevent accidents by monitoring the surroundings and determining if the car is getting too close to other objects or people. In addition to location and distance information, stereo cameras can provide the actual size of objects by applying the determined distance between the object and the stereo camera to the size of the object, as measured in the image. This feature is useful in applications requiring object recognition, such as surveillance, machine vision, and robotic equipment.
Many stereo camera applications either require or can benefit from a miniaturized device, and optics manufacturing technologies capable of producing miniaturized devices, e.g., micro lenses, have been developed. Stereo cameras based on pairs of centimeter-sized camera systems produced using micro optics manufacturing methods are available. However, for a stereo camera, the miniaturization implies a small distance between the two cameras, which in turn places high demands on both the system tolerances and the quality of the recorded images. In order to perform accurate triangulation using two cameras placed very close to each other, the relative positioning of the two cameras and the imaged location of objects in the two captured images must be known or determined with high accuracy.